A roll bending machine consisting of two rolls (hereinafter referred to as the two-roll bending machine) capable of forming works or workpieces into arc- or ring-shaped products of desired diameter.
The conventional two-roll bending machine is of such basic constitution that one of the two adjacent rotatable rolls (hereinafter referred to as the pressured roll) comes under an adjustable pressure from the other of two rolls (hereinafter referred to as the pressure roll). To obtain an arc-shaped product in this system, the work is inserted and passed between the two rolls rotating under squeezing pressure, during which process the work is subjected to a converging pressure from the pressure roll in the direction of the pressured roll, thus undergoing a plastic deformation in such an arc as to wrap about the pressured roll.
In this conventional system, a pressured roll with a small diameter must be used to obtain a formed product of relatively small diameter, and a pressured roll of a large diameter to obtain the product of a relatively large diameter.
In obtaining formed products of the same diameter, however, the conventional system requires a number of pressured rolls of different diameters, depending on the variations in the material, hardness, shape (width, thickness), etc. of the works.
This is because there exists the following relationship between .rho.: radius of the work during forming, .rho.: radius of the work after the springback after forming (outward return of the arc), M: bending moment to work on the work, E: modulus of direct elasticity and I: second moment of area: EQU 1/.rho.', 1/92-M/EI
Here, M, a variable, changes with the desired diameter, the material, hardness and shape (width, thickness) of the work as well as with the work hardening index and plasticity coefficient of the work. E, which is also a variable, changes with the material of the work. And I, another variable, changes with the shape (width, thickness) of the work. To obtain a formed product of a desired radius .rho.' after springback, therefore, it is necessary to change the radius .rho. of the work at forming, namely the radius .rho. of the pressured roll, for every variation in such factors as the material, hardness, shape (width, thickness) of the work which can in turn change M, E and I. Hitherto, however, changing the radius .rho. of a single pressured roll for every variation in the above-mentioned factors has been either beyond thought or considered impossible. Hence, a number of pressured rolls with different radii were prepared and for each variation in the factors a pressured roll of an appropriate radius was selected, or manufactured as required, to perform the forming operation.
Preparation of a number of pressured rolls with different radii as described above requires great expense while manufacture of pressured rolls with optimal radii calls for long experience and advanced technology.
Furthermore, it takes great trouble and time in actual operation to determine a correct radius for the pressured roll according to the delicately varying material, hardness, shape (width, thickness), etc. of the work and then select, or manufacture a necessary pressured roll using long experience and advanced technology. These are the greatest drawbacks found with the conventional two-roll bending machine, which have long awaited solution.
To solve the above-mentioned problems of the conventional two-roll bending machine, the inventor of this machine has devised a novel system as described below.
With the present invention, the work, passed between two rolls rotating under squeezing pressure, is formed into such an arc as wraps about one of the rolls and then, on the exit side where the work is released from the squeezing pressure, the work is subjected to a further forming by a pressure member with a different radius of curvature, provided between the work and the above-mentioned roll, which unbends the passing work to a certain degree.
The novel two-roll bending machine thus presents its practical benefit in the absence of pressured roll replacement conventionally required in obtaining a formed product of desired diameter in compensation for the slight variations in the material, hardness, shape (width, thickness), etc. of the work.
Also, by changing the position of the pressure member, the novel two-roll bending machine using a single pressured roll can produce formed products of the same desired diameter even when there are some variations in the material, hardness, shape (width, thickness), etc. of the works.
Further, the inventor of the present machine has invented the following device which not only solves the problems of the conventional two-roll bending machines but also makes improvements on the aforementioned system.
This improvement relates to a device capable of moving the point of contact between the pressure member and the work during operation in the two-roll bending machine which forms the work into such an arc as wraps about one of the rolls as it is passed between the two rolls rotating under squeezing pressure and then, on the exit side where the work is released from the squeezing pressure, subjects the work to a further forming as the passing work is unbended to a certain degree by a pressure member provided between the work and the above-mentioned roll. And this device makes it possible to build an automated system which, while using a single pressured roll, can produce formed products of a desired diameter.
In application of this device, however, the shape, especially the thickness, of the pressure member and the positioning of the pressure member in actual operation are subject to limitations, beyond which the progress of the forming operation is impeded.
In other words, the thicker the pressure member is, or the closer the pressure member is to the point of tangency between pressure roll and pressured roll during operation, the greater will be the degree at which the work is unbended. And if the pressure member is too thick, or if even a relatively thin pressure member is located too close to the above-mentioned point of tangency, the front end of the work will bump against the pressure member, thus impeding the forming operation.
Therefore, the shape, especially the thickness, of the pressure member and the position of the pressure member during operation have their limits, and the resulting diameter of formed products has its limit also.
In the inventor's test operation, to obtain formed products of a diameter larger than the above-mentioned limit, the work had to be inserted as far as where the front end of the work would not bump into the pressure member, before the squeezing pressure was applied between the pressure roll and the pressured roll, or the pressure member had to be first located in a raised position and then brought down into contact with the work after the front end of the work had passed it, to avoid collision between the front end of the work and the pressure member. That is, an additional work process was required.
Also with the aforementioned system, where the initial contact of the work with the pressure member is not continuous but sudden, it was found that the projection of the pressure member can sometimes damage the work and the pressure member itself is susceptible to wear.